Crimping, which is a special kind of beading, is a method for joining parts, in particular a wire with a connector (often having the shape of a plug), by plastic deformation. The resulting permanent joint provides good electrical and mechanical stability and is thus a suitable alternative to other connecting methods such as welding or soldering. Hence, common fields of application for crimping are electric devices (e.g. for telecommunication, electrical equipment for vehicles, etc.). The shape of a crimp should exactly be adapted to the wire so as to provide for a predetermined deformation of the same. Crimping usually is done by a crimping gripper or a crimping press.
According to prior art, the force acting during the crimping process can be measured to monitor and/or ensure a constant quality of crimp connections manufactured by a crimping press. For example, pressure sensors are utilized for this reason, which measure the force between the frame and the die and/or the drive and the plunger. A further possibility is to evaluate the deformation of the frame.
While the measuring methods mentioned hereinbefore turned out to be notably suitable for crimping presses, further possibilities for the measurement of pressure forces are known in principle from other, outlying technical areas.
For example, JP 091 53676 discloses a device for soldering electronic devices onto a printed circuit board. A heating element is forced onto the electronic device so as to cause the soldering. These or similar devices are also referred to as “thermodes”. The force, which acts on the heating element, is measured by means of a strain gauge attached to a beam, which is asymmetrically loaded.
Furthermore, DE 10 2004 035 246 B3 discloses a force sensor for a press, wherein the force acting on a plunger is measured by an optical sensor, which monitors the bending of a leaf spring.
EP 0 044 191 A1 discloses yet another solution for measuring a load via the deformation of a leaf spring, in particular for measuring the loads acting on a vehicle. In this configuration, strain gauges are used to perform the measurement.
Finally, DE 43 30 808 A1 discloses a sensor to monitor the load acting on a tool by means of the bending of a beam, which is arranged between the tool and a frame. The sensor measures the distance between a bent beam and an unloaded beam.
Unfortunately, the crimping presses known in the art have disadvantages insofar as the force measurement by evaluating the deformation of the frame is relatively inaccurate because the measurement takes place off the plunger and the die. Thus, the measurement result includes a lot of disturbing influences. The measurement by means of pressure sensors circumvents this problem but generates another one because pressure sensors are technically complex and thus expensive. Because of their complexity, pressure sensors are furthermore more prone to failure.
Moreover, solutions known from other, outlying technical areas cannot be used for crimping presses either. For example, the solution known from JP 091 53676 needs relatively complex guidings inducing a lot of bearing clearance because of the asymmetrically loaded beam. A measuring unit having bearing clearance to such an extent is not suitable for a crimping press, where the die and the plunger have to be aligned very exactly. Furthermore, the magnitude of the forces exhibited by a thermode is much lower than by a crimping press because the joint is not caused by mechanical deformation but by liquefaction of a solder. Concluding, the solution known from JP 091 53676 cannot be adapted for crimping presses in principle.
The solution known from DE 10 2004 035 246 cannot be used for crimping presses either because the indirect, optical measurement of the bending of a leaf spring implies relatively strong deformations of the same. Accordingly, it is not possible to measure the force and the travel distance of the plunger at the same time. However, this combined measurement usually is required for crimping presses because in addition to the condition that a particular force or a particular force progression should be met for a high-quality crimp there is also a need to meet a particular travel distance of the plunger. If the plunger travels too far, the crimp gets damaged, if it does not travel far enough, the crimp may be loose. Accordingly, the leaf spring of DE 10 2004 035 246 is not suitable for crimping presses. The arguments discussed for DE 10 2004 035 246 are equally applicable to EP 0 044 191 A1 and DE 43 30 808 A1 because these measurement methods also involve relatively strong deformations. Leaf springs for vehicles, as they are disclosed EP 0 044 191 A1, are traditionally designed to perform a strong bending so as to make travelling more comfortable. The same counts for DE 43 30 808 A1 because measuring the load via the distance between a bent beam and an unloaded beam either requires a long beam or a soft (loaded) beam so as to cause a substantial measuring distance. Both is not suitable for crimping presses.